Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $189.52   8.685%   $205.9798   $205.98   $206.00   $206.00  
  Purchase #2 $211.86   9.462%   $231.9062   $231.91   $231.90   $231.90  
  Purchase #3 $56.80   3.605%   $58.8476   $58.85   $58.85   $58.80  
  Purchase #4 $232.29   3.638%   $240.7407   $240.74   $240.75   $240.70  
  Purchase #5 $89.52   13.594%   $101.6893   $101.69   $101.70   $101.70  
  Purchase #6 $34.74   6.275%   $36.9199   $36.92   $36.90   $36.90  
  Purchase #7 $129.39   12.220%   $145.2015   $145.20   $145.20   $145.20  
  7 purchase totals = $944.12       $1,021.2850   $1,021.29   $1,021.30   $1,021.20